Development of electric vehicles (EVs) and hybrid electric vehicles (HEVs) is in the forefront of automotive research and recent advances in the industry have led to such vehicles in commercial utilization. Ongoing efforts to provide vehicles having the power and range of combustion engine based vehicles have led to advancement of energy units as power supply. New electrical energy charge and discharge systems are under investigation as well as methods of improvement of capacity of conventional battery systems. One issue identified as important to performance of battery modules or battery packs is thermal management of the unit.
Thermal management is very critical to maintain the performance of the battery pack of an electrified vehicle. There are two main issues related to the thermal stress to the battery pack. The first is that the high temperature during charge and discharge will lead to the possibility that temperatures will exceed permissible levels and decrease the battery performance. The second is that uneven temperature distribution in the battery pack will lead to localized hot spots and subsequent deterioration. Temperature uniformity, within a cell and from cell to cell, is important to achieve maximum cycle life of the individual cells, the module and the battery pack. Conventionally, a thermal management system may be passive (i.e., only the ambient environment is used) or active (i.e., a built-in source provides heating and/or cooling), and can be also divided into four categories based on medium:
(i) Air for heat/cooling/ventilation;
(ii) Liquid for cooling/heating;
(iii) Phase change materials (PCM).
(iv) Combination of above.
Thermal management of batteries employing conventional systems (i) and (ii) are reviewed by Pesaran (Advanced Automotive Battery Conference, Las Vegas, Nev., Feb. 6-8, 2001). A review of the use of phase change materials and their utility for thermal management of vehicle components is provided by Jankowski et al. (Applied Energy, 113 (2014) 1525-1561)
Air forced convection cooling could mitigate temperature rise in the battery. However, if the battery temperature rises higher than 66° C., it would be difficult to cool it to below 52° C. by air-cooling, especially when the ambient temperature is high (i.e. greater than 40° C. such as in a desert environment). Furthermore, at stressful and extreme use conditions, especially at high discharge rates, air-cooling will not be sufficient, and non-uniform distribution of temperature on the surface of the battery becomes inevitable.
Liquid cooling requires complicated systems and potential leak of the coolant is always a concern. Such systems add weight to the vehicle and require maintenance. Economic impact on the total cost of the vehicle is also to be considered.
Phase change material systems offer certain advantages over air and liquid coolant systems which include reduced peak temperatures, better temperature uniformity, and reduced system volume. However, PCM systems lead to heat accumulation and significant additional weight. The heat accumulated within the phase change material still needs to be dissipated into environment via other cooling methods, such as air cooling.
Accordingly, there is a need for an effective and efficient thermal management system especially for battery packs for electric vehicles. The thermal management system should contribute minimum weight to the vehicle and should occupy minimum space relative to the size of the battery pack. It should require minimum or no maintenance and should contribute only incremental cost increase to the total cost of the vehicle. An object of this disclosure is to provide a thermal management method and system which meets these needs.